#include<stdio.h>
int main()
{
	int num = 0,sum=0,score=0;
	float averge = 0;
	while (score != -1)
	{
		scanf_s("%d", &score);
		if (score == -1)
			break;
		else
			num++;
		sum += score;
		averge =(float) sum / num;
	}
	printf("%.3f", averge);
	return 0;
}